This invention relates generally to digital computer memories and more particularly to digital computer memories which are made up of a plurality of data storage components.
As is known in the art, microprogram controlled digital computers generally include a microinstruction memory for storing a plurality of microinstructions. Each stored microinstruction generally includes a plurality of fields, each field corresponding to one or more bits in the stored microinstruction. Each bit is represented by one of two logical states. If there are N bits in each microinstruction and if M microinstructions are to be stored in a microinstruction memory, or NxM microinstruction memory has heretofore been designed. Further, it is known that generally many stored microinstructions have a particular field, or portion thereof, which includes a plurality of bits, each being represented by the same logical state.
The microinstruction memory is generally of the "read only" type. Since read only memory (or data storage) components readily available in the marketplace are generally limited to a maximum of 1024 or 2048 addressable words (or locations), each eight bits in length, and many microprogram controlled digital computers require microinstructions which are greater than eight bits in length and more than 2048 addressable words or microinstructions, a plurality of read only memory or data storage components is required to provide the requisite microinstruction storage capacity. Because the cost of each one of the read only memory components adds to the overall cost of the computer, it is desirable to minimize the number of read only memory components required in such computer.